1. Field of the Invention
This invention generally relates to devices and methods of controlling the function and smoothness of action involved in many mechanical movements. This invention is related to sliding surfaces both linear and rotational and involves the use of controlled magnetic forces.
2. Description of the Prior Art
Many methods and devices have been utilized in the production of accurate, smooth acting, low resistance sliding mechanisms, such as dovetail slides with adjustable jib, ball bearing slides, rotating bearings in retainer and continuous array for linear movement and rotational movement. Although lubrication of bearing surfaces is important in producing smooth low friction movements, precision machining is paramount in producing accuracy as well as smoothness of operation. Precision air bearings and bearings in vacuum are often considered as the ultimate in reducing friction.
Other factors besides reduced friction are of consideration in producing a desirable sliding or rotating action. Too free a movement, particularly when the moving element requires adjusting or setting to a desired position often results in "overshooting" or hunting, to reach the desired position. Too free a movement can contribute to "back lash" and instability in holding on a desired position. Therefore a certain amount of resistance to movement is often desirable and many devices are presently provided with means of controlling resistance--such as the well known "jib" on a conventional undercut and lubricated dovetail slide.
This present invention describes how magnetic forces can be used in controlling the action, feel, sticking and friction of sliding surfaces in a simple adjustable manner which does not necessarily require highly precise machining of the related parts. Magnetic forces are being used in some situations today, in some devices, but not in a manner whereby the magnetic forces can be mechanically adjusted so as to achieve the desired smooth action.
A "magnetic-kinematic" principle is presently being used by Physik Instruments (PI) (U.S. Pat. No. 3,720,849 to Bardocz) in a design of their micropositioner to assist in achieving extremely high precision and accuracies of positioning in the sub-micron range where .+-.0.000005 inch are required. Part of their design incorporates what they call "magnetically-coupled" ball bearing slides in which the two sides of the slide are held together against ball bearings by internal magnets separated by a few tenths of a millimeter. This separation distance is not adjustable. Therefore the performance of the slide is determined at tile factory.
In my invention, sub-micron accuracies are not an objective. Controllability and adjustability as well as economy of production are some of the objectives as will be seen in this specification. The above PI system does not provide adjustability and is considerably more expensive to produce than are devices produced in accordance with this invention. Some of the devices and parts described in this invention can even be molded not machined. While ball bearings can be used, they are not necessary.
In addition to the field of micropositioners, smooth acting relatively accurate sliding devices and mechanisms are utilized in many areas, such as door slides, drawer slides, computer mouse input devices, microscope stages as well as larger stages, positioners used in manufacturing, optical equipment, cameras and accessories, etc.
The techniques and devices described in this patent have many applications. In most cases the parts and mechanisms required can be made of molded plastic. These devices and mechanisms can be made to replace or substitute for more expensive devices such as dove tail slides, rack and pinion, adjustments, continuous ball bearing slides, high load resistant bearings, etc.
Other patents which utilized magnetic forces to assist in the action of sliding mechanisms are as follows:
U.S. Pat. No. 4,065,188--Linear Bearings for Parallel Tracking Arm PA1 U.S. Pat. No. 4,570,249--Optical Read/Write Head for Recording and Playback of an Optical Disk and an Optical Device Associated with said Optical Head PA1 U.S. Pat. No. 4,704,712--Low-Friction Apparatus for Optical Disk Translation Stage PA1 U.S. Pat. No. 3,789,285--Position Control System Using Magnetic Force
In all of the above patents magnetic forces are used but not in the manner of my invention and in none of the above patents as well as the "PI" "Magnetic-Kinematic" principle (see previous paragraph) is the sliding action adjustable as it is in my invention.
In U.S. Pat. No. 4,065,188 magnetic forces are used to hold a lubricant in position between a bearing surface and a moveable bearing surface. This is accomplished by incorporating magnetic material in the lubricating material so that it is attracted by magnetic forces to one of the bearing surfaces. This device is not adjustable in the sense that my present invention is.
In U.S. Pat. No. 4,570,249 a system of magnets and conductors are arranged such that an electric current on an adjacent surface will produce a magnetic field repulsive to the magnetic field generated by the magnet on the other surface and thus move one surface with respect to the other. This is in no way an adjustable sliding bearing of the type described herein.
In U.S. Pat. No. 4,704,712 magnetic forces are used in a sliding bearing to provide a low friction device that incorporates air bearings, the magnetic forces are used to maintain a consistent position of the sliding surface as it moves along the magnets incorporated in a rail. The magnetic forces hold the sliding member close to the rail so that the air, escaping through small openings, which force the sliding member away, is counteracted thus providing an air bearing. An electric linear motor provides the motivating force to the sliding member. This is not a simple sliding system in which the "feel" of the sliding action is controllable as in my invention.
In U.S. Pat. No. 3,789,285 the electromagnets are not permanent magnets as in my invention, but are used to provide a motivating force to adjust the position of one member with respect to another by controlling the electric current that activates the magnets. In my invention the motivating force can be by human adjustment of a screw (micrometer), cam, lever or it can be electrical such as a magneto ceramic positioner, linear motor, or it can be pneumatic, hydraulic, etc. In my invention permanent magnets are utilized and the spacing is adjusted to provide a smooth acting "feel" to the movement of a sliding device. This invention also does not apply to magnetic bearings which are intended to almost completely eliminate friction and the need for lubrication.